This invention relates to apparatus for launching electromagnetic waves in any one of a plurality of modes of polarization and, more particularly, to a system for electrically selecting a desired mode of polarization.
In the processing of electromagnetic signals, it is frequently desirable to combine signals of various phases and polarizations to produce a resultant signal having a desired polarization. A typical example of such signal processing occurs in the generation of a circularly polarized electromagnetic wave radiated from an antenna. It is common practice to generate such a circularly polarized wave by combining two component signal waves in phase quadrature and having their electric vectors oriented perpendicularly to each other and to a direction of power flow. An equality in the amplitudes of the two component signals produces a circularly polarized resultant wave, while an inequality in the amplitudes of the two component signals produces an elliptically polarized wave. Interchanging the sine and cosine relationships of the two component waves reverses the direction of the circular or elliptical polarizations. In addition, activation of only one of the component waves produces a resultant linearly polarized wave. In some applications, it is desirable to have the facility to switch from one polarization to another polarization of the resultant outputted electromagnetic wave.
A problem arises in that presently available switching systems for altering the component signals have been limited in the number of possible polarizations which can be selected. The introduction of additional microwave circuitry to provide for the capacity to select additional polarizations for the resultant signal has resulted in an undesirable increase in complexity and physical size to microwave equipment employed in the generation of the resultant signal.